Data processing apparatus for chromatograph

ABSTRACT

A method of properly correcting a base line. A concept of flexibility of a base line is introduced as an input index and a gravitation is presumed between the base line and signal data which is measured, thereby constructing a method of correcting the base line which changes gentler than a change in signal with respect to time in a peak area and which is sensitive to an area where a value of the signal data is small. A base line like a natural and smooth curve which isn&#39;t easily influenced by a local change in signal such as noise or the like can be set by an input of the flexibility.

This is a continuation of application Ser. No. 10/319,692 filed 16 Dec.2002, now U.S. Pat. No. 6,675,107, which is a continuation ofapplication Ser. No. 09/940,636 filed 29 Aug. 2001, now U.S. Pat No.6,529,836, which is a continuation application Ser. No. 09/562,026 filed1 May 2000, now U.S. Pat. No. 6,314,374, which is a continuation ofapplication Ser. No. 08/605,416 filed 22 Feb. 1996, now U.S. Pat. No.6,148,266.

BACKGROUND OF THE INVENTION

The present invention relates to a data processing apparatus for achromatograph and, more particularly, to a method of correcting a baseline.

According to Japanese Patent No. 1,385,425 (Japanese Patent PublicationNo. 61-54181), as a method of correcting a base line of non-separationpeaks, there are:

-   -   (1) the N method, (2) the θ method, and (3) the method of merely        connecting a base portion by a straight line (non-correction        method).

In the N method, the number of peaks (N) is designated, N peaks arecollected as one peak, and either a base portion or a trough portion isconnected by a straight line (FIG. 3(A)). The base portion is a portionthat is judged as not a peak area by using a change amount of signal asan index.

In the θ method, an inclination is intentionally loosened when theinclination seems to be too steep in the N method (FIG. 3(B)).

The non-correction method is a most typical method and is effective whenthe base line is estimated to be like a straight line (FIG. 3C). Inaddition, there is also a case of correcting a base line byintentionally selecting a forward horizon method (FIG. 3D), a backwardhorizon method (FIG. 3E), a special processing method of a shoulder peak(FIG. 3F), or the like in accordance with a peak shape of eachchromatogram.

Each of the above base line correcting methods has both merits anddemerits and is selected depending on a particular case, since it isdifficult to unconditionally determine the base line. Although somemethods in which the base line is unconditionally determined have beenproposed (Japanese Patent Application Laid-Open Sho 62-32360, JapanesePatent Application Laid-Open Sho 63-88443, Japanese Patent ApplicationLaid-Open Hei 6-94696, and the like), those methods are not yetgenerally used.

In all of the above methods, the base line is corrected on the basis ofthe base or trough portion existing in the chromatogram.

An algorithm of searching the base or trough portion generally tends tobe too sensitive to a local fluctuation in a signal. For example, a casewhere the trough portion is detected and a case where it is not detectedoccur depending on a magnitude of noise. A detection of a starting pointand an ending point of a peak, that is, an end point detection of thebase portion is also disturbed by noise. After all, such a correction ofthe base line is easily affected by noise and quite different base linesmay be obtained due to a slight difference in signals.

By a similar reason; there is a case where the base line largelyfluctuates when parameters such as sensitivity, slope, and the like, todetect the base portion or trough portion, are improper.

In the case where the base line is experientially estimated to behorizontal, if a horizontal straight line is applied to the baseportion, a proper base line can be obtained. In the case where the baseline may possibly not be horizontal, however, a method of obtaining thebase line by continuing the base or trough portion with a straight linelike a graph of polygonal line is not always proper.

SUMMARY OF THE PRESENT INVENTION

It is an object of the invention to provide a data processing apparatusfor a chromatograph, which solves the above problems, forms a stablebase line without being affected by a local noise of a chromatogram, andcorrects the base line irrespective of local fluctuations of achromatograph.

In a data processing apparatus for a chromatograph comprising base linedetermining means for detecting an output value of a detector for achromatograph obtained with the elapse of time, forming a chromatogramon the basis of the detection result, and determining a base line on thebasis of a shape of the chromatogram, when the base line is corrected, adeviation in the direction of the output value between each of formingpoints which form the base line and a forming point adjacent to theforming point is largely reduced as the deviation becomes larger.

Adjusting means of the base line adjusts so as to reduce a change amountof the deviation proportional to the deviation with an increase in thedeviation and to increase the change amount of the deviationproportional to the deviation with a decrease in the deviation.

Further, an adjusting range of the adjusting means from a base line isdetermined on the basis of the shape of the chromatogram to a linearbase line connecting base lines before and after a time zone in whichthe chromatogram appears as a measuring target appears.

There is also provided selecting means for applying the aboveconstruction to an optional time zone of the measurer.

In the time zone in which the chromatogram appears as a measuring targetsample, the deciding means for deciding the base line on the basis ofthe shape of the chromatogram decides the base line on the basis of adistance on the same time base from either one of a straight lineconnecting a starting point and an ending point of the time zone inwhich the chromatogram appears, a straight line connecting the startingpoint and the trough portion of the chromatogram, and a straight lineconnecting the ending point and the trough portion of the chromatogramto the chromatogram, and arranges a forming point of the base line so asto shorten a distance on the same time base from the straight line forthe distance to the base line with an increase in the foregoingdistance.

In one mode of the arrangement of forming points on the base line, thebase line is set to the same line as the chromatogram in the time zonein which the foregoing distance is equal to a value which ranges fromzero to a predetermined value.

The base line of the chromatogram inherently has a very loose change ascompared with the signal change in the peak area and its change width isnarrow.

That is, when the base line is regarded as a collection of a pluralityof points, it is considered that two neighboring points among the pointsare loosely bound to each other. Namely, a base line of a shape having alocal projection is impossible. If the base line having a localprojection is drawn, it is considered that the portion is projected dueto improper drawing means of the base line or an influence by noiseoccurring somewhere in a chromatograph device.

In consideration of the above, when the base line drawn by various meansis regarded as one line constructed by a plurality of points, thecorrection is performed so as to reduce a deviation in the direction ofthe output value between the two adjacent points among the points as thedeviation becomes large, so that the base line adapted to the abovecondition can be drawn.

The base line drawn as mentioned above can be adjusted while maintaininga gentle line in a manner such that when the deviation between the twopoints in a time zone is increased, a change amount of the deviation isreduced in proportion to the increase in the deviation and, when thedeviation is reduced, the change amount of the deviation is increased inproportion to the decrease in the deviation.

Another characteristic of the base line is such that the base line isstrongly attracted to an area in which a signal value expressed by thechromatogram is small.

It is because the signal value that is caused by another component whichis a factor of the noise is unlikely to appear in the time zone in whicha target component appears and an output value which is not so large isgenerated since it corresponds to an amount of noise after all, and thelike.

In consideration of the above, the base line corresponding to the abovecharacteristic can be drawn by arranging the forming points of the baseline in a manner such that as the distance in the time base directionfrom the chromatogram to the base line as a reference (linear base lineconnecting base lines before and after the time zone in which thechromatogram as a measuring target appears) becomes longer, a distancein the same time zone from the straight line for the foregoing distanceto the base line is largely reduced.

When the drawing means of the base line and the correcting means of thebase line are used together, since the projected portion of the baseline drawn by the drawing means can be corrected by the correcting meansof the base line, the correction of the base line in which the twocharacteristics of the base line are considered can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of a physical model of theinvention;

FIGS. 2A-2B are diagrams showing problems of a conventional method;

FIGS. 3A-3F are diagrams showing a conventional method of correcting abase line;

FIG. 4 is a diagram showing a construction of a data processingapparatus according to an embodiment of the invention;

FIGS. 5A-5B are diagrams showing output examples of a chromatogram;

FIG. 6 shows an input screen of gravitation types;

FIG. 7 shows a profile of a gravitation of a step function type;

FIG. 8 is an explanatory diagram of advantages of the embodiment of theinvention;

FIGS. 9A-9B are diagrams showing an example of a time program offlexibility;

FIG. 10 is a diagram showing an example of a connection of baseportions;

FIG. 11 is a diagram showing an example of a separation of a shoulderpeak;

FIG. 12 is an explanatory diagram of a base line envelope method;

FIG. 13 is a diagram showing an overlay of a base line;

FIG. 14 is a diagram of an output example showing reproducibility of aquantitative value;

FIG. 15 is a flowchart showing a condition setting for a base linecorrection before a signal is taken in;

FIG. 16 is a flowchart showing a condition setting for the base linecorrection after a signal is taken in;

FIG. 17 is a flowchart 1 showing a condition setting for the base linecorrection;

FIG. 18 is a flowchart 2 showing a condition setting for the base linecorrection;

FIG. 19 is a flowchart 3 showing a condition setting for the base linecorrection;

FIG. 20 is a flowchart 4 showing a condition setting for the base linecorrection;

FIG. 21 is a flowchart 5 showing a condition setting for the base linecorrection;

FIG. 22 is a flowchart 6 showing a condition setting for the base linecorrection;

FIG. 23 is a flowchart 1 showing an over display of a base line;

FIG. 24 is a flowchart 2 showing an over display of a base line;

FIG. 25 is a diagram showing an overlay of the chromatogram;

FIG. 26 is a diagram showing a manual pick up method;

FIG. 27 is a flowchart 1 showing the manual pick up method;

FIG. 28 is a flowchart 2 showing the manual pick up method; and

FIGS. 29A-29D are explanatory diagrams of a second base line envelopemethod.

DETAILED DESCRIPTION

An embodiment of the invention will be described hereinbelow withreference to FIG. 4. FIG. 4 is a block diagram of a data processingapparatus for a chromatograph to which the invention is applied. In FIG.4, reference numeral 1 denotes a central processing unit (CPU); 2 aperipheral equipment connecting unit; 3 an A/D converter; 4 a signaldata memory; 5 a control command memory; 6 an input device; 7 an outputdevice; 8 a result data memory; 9 a process parameter memory; and 10 adetector for a chromatograph.

An analog signal from the detector 10 for a chromatograph is convertedto a digital signal by the A/D converter 3 and is supplied to the CPU 1through the peripheral equipment connecting unit 2. By a command in thecontrol command memory 5, the signal is converted to signal data of apredetermined format and the data is stored into the signal data memory4.

An embodiment of forming means of a base line of a chromatogram andcorrecting means of the base line of the formed chromatogram of theinvention will now be described.

According to the embodiment, the base line is formed and corrected onthe basis of two characteristics of the base line of the chromatogram.The two characteristics are such that the base line is stronglyattracted to an area in which a signal value expressed by thechromatogram is small and that neighboring points in the base lineformed by continuous points are loosely bound.

The former characteristic is coped with in a manner such that as adistance between each of continuous points which form the chromatogramand a forming point of a reference base line (in the embodiment, a lineobtained by connecting base lines before and after a time zone in whicha peak of a measuring target sample appears) in the same time basedirection becomes large, a ratio of length between the straight line forthe distance and the forming point of the base line is reduced.

That is, as the reference base line on the same time base becomes closerto the chromatogram, the reference base line is strongly attracted tothe chromatogram. It can be defined that gravitation or magnetism actsbetween the chromatogram and the reference base line on the same timebase from this point of view, since when the distance is long, only aweak force acts, and when the distance is short, a strong force acts.

The latter characteristic is coped with in a manner such that the longera distance in the time base direction between the adjacent points amongthe continuous points which form the base line is, the more the distanceis reduced.

When a physical idea is adapted to the above, the characteristic ofspring can be considered since the more a spring is stretched, thestronger a force acts.

A formation of the base line in consideration of the two characteristicsof the base line will now be considered.

FIG. 1 is a diagram showing a specific physical image considering thetwo characteristics. Although a two-dimensional elastic body (spline) orplastic body (adjustable ruler) or the like can be introduced as a baseline, the formation of the base line is considered here in a category ofdynamics of a one-dimensional elastic body, particularly, statics inwhich a balance of forces used for simplicity of explanation.

A signal waveform doesn't move and points each having plus charges arefixed at equal intervals. Particles having minus charges are arranged onthe base line so as to correspond to the plus charges. It is now assumedthat a Coulomb force acts only between the plus and minus charges on thesame x-coordinate. The particles of minus charges cannot freely move andthe neighboring particles are connected by a spring. A model wherein twoor three neighboring particles are weighted and connected by a spring isalso possible. It is also assumed that elasticity of the spring worksonly in the vertical direction (Y direction). That is, axes attached toblank circles in FIG. 1 move only in the vertical direction and don'trotate.

The straight base line is horizontally lifted from the lower part ofsignal data. The straight line is rotated by using a point which iscontacted for the first time as an axis and a point to be contacted nextis obtained. The straight line is rotated right and left and a contactpoint which is located further from the axis is used. A gravitation isacted in this instance and the base line is allowed to be curved. Thesignal data and the base line make contact at a point where thegravitation acts more than the elasticity of spring which acts againstto be curved.

Expression 1 shown below is a balance equation of force on an optionalx-coordinate.

-   -   balance equation of force: $\begin{matrix}        {{{K\quad\frac{q^{2}}{\left( {Y_{i} - y_{i}} \right)^{2}}} - {k\left( {y_{i} - y_{i - 1}} \right)} - {k\left( {y_{i} - y_{i + 1}} \right)}} = 0} & \text{[expression~~1]}        \end{matrix}$        where,

-   K: constant of Coulomb force

-   Y_(i): (i)th signal data point (constant)

-   q: charge (constant)

-   y_(i): (i)th base line point (variable)

-   k: spring constant

The condition is Y_(i)≧y_(i). When Y_(i)=y_(i), the balance equation isunnecessary.

Y_(i−1), Y_(i), Y_(i+1), and the like are variables and the others areconstants. A point where an actual signal value Y_(j) and a base liney_(j) are equal, namely, a point of contact is eliminated from thebalance equation and the number of equations is set to n. Although nvariables can be obtained from the n balance equations, it is moreefficient to solve the equation by approximating it to a linear equationsuch as Y_(i) or the like as shown below. When Y_(i)>>y_(i):$\begin{matrix}{{{\frac{K_{q}^{2}}{Y_{i}^{2}}\left( {1 + \frac{2\quad y_{i}}{Y_{i}}} \right)} - {k\left( {y_{i} - y_{i - 1}} \right)} - {k\left( {y_{i} - y_{i + 1}} \right)}} = 0} & \text{[expression~~2]}\end{matrix}$

The base line obtained as mentioned above is shown by blank dots in FIG.1. Although the number of dots expressed is small in FIG. 1, acalculation is actually performed by using all of the sampling points.By correcting the base line with such a model, the base line isn'texcessively curved and the base line which is properly contacted andclose to a portion where the signal value is small can be obtained. Thatis, flexibility of the base line is characterized by parameters ofstrength of materials such as spring constants and the like, therebypreventing a rapid local change. The signal data and the base line areattracted by a gravitation force having a distance dependency such asthe Coulomb force or the like, so that the base line can be broughtespecially strongly close to an area where the value of the signal datais small.

In case of actually properly correcting the base line by data processingapparatus, an index such as strength of flexibility is input as aparameter like the spring constant and a distance dependency ofgravitation (inverse-square type, exponential function type, stepfunction type, and the like) is designated.

Although the base line has been formed and corrected on the basis of thetwo characteristics of base line in the illustrated embodiment, the baseline can also be formed and corrected by taking account of only one ofthe two characteristics.

That is, it is also possible to form the base line by base line formingmeans as in the conventional technique, input the index of strength ofthe flexibility, such as spring constant, as a parameter, according tothe invention, smooth a projected portion in the base line obtained byusing the base line forming means which depends on the distance betweenthe chromatogram and the reference base line of the invention, and thelike.

Various concepts can be included in the base line correction accordingto the embodiment of the invention as mentioned above. Selecting meanswill now be described in accordance with the order of steps of the baseline correction.

Parameters for the base line correction have preliminarily been storedinto the process parameter memory 9 from the input device 6 before asignal is taken in (FIG. 15). The following inputting operation will bealso similarly executed in a case of again performing the base linecorrection to the signal data once taken in (FIG. 16).

The type of gravitation is selected from another picture screen (FIGS. 6and 17). Although a parameter of a gravitation constant has to beinherently set, the input can be omitted since it is in relativerelation to the flexibility of the base line. Parameters regarding adistance (pV) between the signal data and the base line have to beinput. A characteristic distance ro is directly input by a numericalvalue (μV) or can also be automatically set by a peak height, a valuethat is constant times as large as noise, or the like.

The inverse-square type gravitation relates to an interaction generallyexisting in the natural world such as Coulomb force, gravitation, or thelike and has the shape of expression 3, as shown below. The exponentialfunction type gravitation is expressed by expression 4 as shown belowand when the distance becomes long, the gravitation rapidly attenuatesas compared with that of the inverse-square type. $\begin{matrix}{{f(r)} = \frac{1}{r^{2}}} & \text{[expression~~3]} \\{{f(r)} = {\left. {\mathbb{e}}^{{{- r}/r} - 0} \right.\sim\left\{ \begin{matrix}\frac{1 - {\frac{r}{r_{0}}\quad\left( {r{\operatorname{<<}r_{0}}} \right)}}{\begin{matrix}0 & \left( {r{\operatorname{<<}r_{0}}} \right)\end{matrix}} \\\quad\end{matrix} \right.}} & \text{[expression~~4]}\end{matrix}$

It is necessary to input a parameter of a distance r₀ ([(μV). The stepfunction type gravitation is expressed by a profile of a gravitation asshown in FIG. 7. When the distance between the signal data and base linebecomes shorter than the distance r0, the gravitation works. Since thepresence or absence of the gravitation is decided only by judging thedistance (μV), there is an advantage such that a calculating process canbe omitted. An optional expression can be inputted to the function typeand a function which becomes smaller as the distance becomes longer suchas expression 5 shown below or the like can be used. $\begin{matrix}{{f(r)} = \frac{1}{r}} & \text{[expression~~5]}\end{matrix}$

The flexibility of the base line is set by using the CRT output device 7from the keyboard input device 6 as shown in FIG. 5A. Hardness can beadjusted by a cursor key while watching a flexibility bar graph (FIG.18) or the hardness can be also picked up on the CRT. The setting can bechanged by the cursor key to select a proper base line even after thesignal is taken in. Since a medium hard base line is set here, a baseline which is like a straight line is obtained.

From a point of view of strength of materials, the flexibility of thebase line corresponds to a spring constant or a Young's modulus.Actually, the relative elasticity intensity from 0 to 100 is input. When0 is input, the spring loses the elasticity and becomes like a stringand the base line becomes quite the same as the waveform of the signaldata. When 100 or infinity is input, the base line becomes like a stickof a rigid body having a high rigidity or a straight line which contactsthe signal line with at least two points.

In FIG. 5B, baseline elasticity is input by a numerical value from aSOFT key. Since a rather soft base line is set, the base line is morecurved. The chromatogram and a calculation result is sent to the printeroutput device 7 to be printed using a COPY key.

In addition to use of the spring constant as a parameter of flexibility,a correction which minimizes a distortion energy of the base line likean adjustable ruler, a correction like a spline (bar flexibility ruler)which minimizes a whole curve, and the like can be also adapted.

As a derivative method of the step function type gravitation, a baseline envelope method can be considered. An envelope (envelope band) ofthe distance r₀ is provided above and below the flexible base line. Whenthe signal data exists in the envelope, the base line contacts the dataline, or as shown in FIG. 12, when there is an envelope below the signalline, the base line is contacted from the lower part. Such operationsare sequentially repeated, thereby determining the shape of the baseline. In the method, it is also necessary to input the parametersregarding the distance r₀ (μV) in a manner similar to the step functiontype (FIG. 19). This can be regarded as a special case where f0 is equalto infinity in the step function type of FIG. 7. Or, this is almost thesame as a method where an interval in which the change amount of asignal is small is regarded as a base portion and a shape which isdecided when the flexible base line is contacted from the lower part tothe base portion is set to the base line. Further, when the elasticityis set to 0, the base line becomes like a string, a portion which is notcontacted to the data line becomes a straight line as if theconventional non-correction method is used.

As another base line forming means, the base line envelope means shownin FIG. 29 can be also considered.

As shown in FIG. 29A, a straight line is contacted to the chromatogramfrom the lower part with two points (P) and (Q). An envelope line ofdotted line is shown on an enlarged diagram of the (P) point in FIG.29B, points r₁, r₂, and 11 on a time base corresponding to points R1,R2, and L1 on the chromatogram are contacted to the points R1, R2, andL1 on the chromatogram in accordance with the order of FIGS. 29(C) and29(D) and the contacting operation is stopped when a point as shown by apoint r3 which is deviated from the envelope line appears. The aboveoperation is similarly applied to the (Q) point and the base linebetween the (Q) and (P) points is curvedly modified in accordance with avector of the base line having a point contacting the chromatogram,thereby enabling a smooth shaped base line to be drawn.

Advantages of the base line correcting method which is not based on thebase portion or the trough portion will be described by using thechromatogram of glycohemoglobin of FIG. 8 as an example. Hitherto, inorder to correct the base line so that it contacts a trough portionbetween s-Alc and A0, the former six peaks have to be collected in the Nmethod. In actual samples, however, there are not always six peaks. Itcan happen that a trough portion between Ala1 and Ala2 doesn't appear,an F peak disappears, a trough between 1-Alc and s-Alc is not clear, andthe like. Due to this, after taking in the signal data, the number ofpeaks has to be counted again and the N value has to be set again in anoffline post-process. According to the present method, by merely settingthe flexibility to a proper value, a similar base line can be alwaysobtained irrespective of the number of peaks.

When the flexibility of the base line is desired to be changed in themiddle of the chromatogram, it is set by a time program as shown in FIG.9A (FIG. 20). When the flexibility of the base line is input as 70 attime 0.0 minute and 90 at time 2.5 minutes, the flexibility can bechanged in the interval in a linear gradient manner. A setting can bealso performed by subsequently picking up a starting point of the timeprogram and an intensity of flexibility while watching the chromatogramon the CRT.

The flexibility can be also input for an interval by exclusive-use inputitems for the base line correction as shown in FIG. 9B. HARD is set fora period of time from 0.0 to 2.5 minutes and MEDIUM HARD is set for aperiod of time from 2.5 to 7.0 minutes. In this case, although astepwise switching is performed, it is necessary to locally perform agradient switching at a switching point of 2.5 minutes so as not to havean unnatural curve. As it will be understood from this, one value todesignate the flexibility for the whole chromatogram is preferable.

Similarly, the characteristic distance r₀ can be also set by the timeprogram (FIG. 21).

As another embodiment of the invention, a method of detecting a baseportion and connecting the base portion by a smooth curve will bedescribed (FIG. 22). An interval in which the signal change amount issmall is searched as a base portion by using parameters such as noise,sensitivity, slope, and the like. FIG. 10 shows a graph made from thebase portions obtained as mentioned above.

Instead of the conventional method of detecting the base portion on thebasis of the signal amount change as mentioned above, a base portiondecided from the relation of gravitation acting between the flexiblebase line and the signal data line can also be used. A portion where thesignal data line and the base line contact in the foregoing embodimentis regarded as a base portion (FIG. 5). Portions which are not contactedare cut, the base portions are left, and a next connecting processfollows.

In a manner similar to the foregoing base line envelope method, theflexible base line is contacted to the base portion from the lower part,thereby connecting the base portion. A point such that there is theprocess exclusively used for searching the base portion in this case isdifferent from the foregoing base line envelope method. There aredifficulties such that when the rigidity of the base line is too high,an unnaturally curved base line is obtained. When the elasticity is setto be low, the base portion is connected more linearly, and a smoothnesscannot be obtained.

A spline interpolating method is effective to a connection of the baseportion. In a general spline method, data points are smoothly connectedby using a cubic polynomial. Since this case relates to the connectionof the base portion comprising a plurality of points, the process isslightly different. The base portion is regressed by a linear,quadratic, or cubic expression. The quadratic expression is preferable.When the regression isn't successfully performed, points on theconnection side of the base portion are used to regress to the quadraticexpression. A cubic polynomial for interpolation is determined so that0th and first derivatives are equal at an end point on the connectionside of the base portion.

As shown below, an interpolation expression has four unknown letters, a,b, c, and d. When a regression expression y_(i) (x) (expression 7) ofthe base portion on the left side and an interpolation cubic polynomialy(x) (expression 6) make the 0th and 1^(st) derivatives equal at an endpoint L and a similar condition (expression 8) is also requested withrespect to the right side, four expressions are obtained and all of theunknown letters can be determined. The connection conditions in thisinstance for the left-side and right-side regression expressions areshown hereinafter (expression 9).

-   -   interpolation cubic polynomial        y(x)=a+bx+cx ² +dx ³  [expression 6]    -   left-side regression expression        y ₁(x)=a ₁ +b ₁ x+c ₁ x ²  [expression 7]    -   right-side regression expression        y _(r)(x)=a _(r) +b _(r) x+c _(r) x ²  [expression 8]    -   conditions of connection $\begin{matrix}        \left\{ {\begin{matrix}        {{y_{1}(L)} = {y(L)}} \\        {{y_{1^{\prime}}(L)} = {y^{\prime}(L)}}        \end{matrix}\left\{ \begin{matrix}        {{y(R)} = {y_{r}(R)}} \\        {{y^{\prime}(R)} = {y_{r^{\prime}}(R)}}        \end{matrix} \right.} \right. & \text{[expression~~9]}        \end{matrix}$

The connection of the base portion can be consequently performed by thespline interpolation method.

As another embodiment, a case of the shoulder peak will be described.The spline interpolation method is also used in principle in the case.As shown in FIG. 11, the right and left regression expression of theshoulder peak are smoothly connected by the interpolation expression,thereby enabling a parent peak and the shoulder peak to be separated. Inthis case, a starting point of the shoulder peak is a trough portion andan ending point is, for the convenience, a point of contact when atangent line is drawn from the trough portion to a foot portion of theparent peak.

As a last embodiment, a method of manually correcting the base line willbe described. A point where a base line is likely to exist is picked upwhile watching the chromatogram on the CRT (FIG. 26). Although a methodof spline interpolating the picked point can also be considered, themethod depends on the picked point too much. A method of using theflexible base line is also effective (FIG. 27). In this case, thegravitation is allowed to act downward from the data line to the baseline and the gravitation is also allowed to act in the verticaldirection between the picked point and the base line. Since it ispreferable that the base line and the picked point don't largelyseparate, the gravitation of a type which acts stronger as the intervalbetween them becomes longer is selected. For example, a gravitationwhich is proportional to an absolute value of r² or r is suitable. Inthis case, an input of a gravitation constant is necessary. The twokinds of gravitations and flexibility are considered and the balanceequation is solved, thereby determining the optimum flexibility.Consequently, the base line which is imaged by the operator can beobtained. According to such a method, the correction can be similarlyperformed even when a curve like an outline is input.

An example such that three kinds of base lines when respectiveflexibility i's used are overlaid and displayed is shown in FIGS. 13 and25 (FIGS. 23 and 24). According to the manual pick up method, the properbase line can be selected from the various base lines displayed on theCRT as shown in FIG. 13. Further, by preliminarily picking up a presumedcross point of the base line, the optimum flexibility can be calculated(FIG. 28).

When the base line is determined as mentioned above, a quantitativecalculating process follows. A height or area is used as a peak size.When the calculation is executed on the basis of the peak height, avalue obtained by subtracting a base line Y_(i) from a signal valueY_(i) at a point where the peak is largest is set to the peak height(FIG. 3).

When the calculation is executed on the basis of the peak area, an areacalculation is performed according to the trapezoidal rule or Simpson'srule after obtaining Y_(i)−y_(i) with respect to all of points in thepeak area.

It is often necessary to confirm reliability of an obtained quantitativevalue. As shown in FIG. 14, coefficients of variation or a relativestandard deviation of the quantitative value in each of theflexibilities are output in a format of a table, so that thereproducibility of the quantitative value can be recognized. It will beunderstood from the table that good reproducibility can be obtained whenthe medium flexibility is selected in the case.

In addition to the table in which the reproducibility is arranged forevery flexibility, a table in which various quantitative methods arecompared is also effective. For example, the quantitative method basedon the peak area and that based on the peak height, or the conventionalbase line correcting method and the method according to the inventioncan be compared.

When the base line is formed or corrected, since the base line in whichthe two characteristics of the base line such that the base line isstrongly attracted to the area having the small signal value expressedby the chromatogram and that adjacent points among continuous pointswhich form the base line are loosely bound are considered can be formed,the base line which is more natural and is not influenced by noise andthe like can easily be drawn by anyone and the base line that is alwaysstable can easily be provided without a special operation by theoperator.

By introducing the index of the flexibility that is one of thecharacteristics of the baseline, the base line which is not theconventional temporary base line like a graph of polygonal line but of amore natural and smooth curve can be obtained.

Although the base line has conventionally been corrected on the basis ofdifferential characteristic points of a signal such as starting andending points of a peak, trough between peaks, and the like, the baseline which is not especially influenced by the fluctuation of such kindsof characteristic points can be obtained in the invention, so that themethod is not much affected by local changes and noises.

Thus, the peak size can be accurately determined and the stablequantitative calculation can be always executed.

1. A chromatograph comprising: a detector for detecting a sample so asto output a measuring signal according to elapsed time, an input unitfor inputting a strength parameter characterizing a form of base line byan operator, a data processor for processing said measuring signal basedon said information signal so as to output a chromatogram formed with aplurality of chromatogram data points and a base line corresponding tosaid chromatogram, said data processor correcting a plurality of datapoints forming said base line based on said strength parameter, saidstrength parameter defining a difference in a direction of signalstrength of said chromatogram between adjacent data points of said baseline, and a display for displaying said chromatogram and said base line,said display having a strength parameter display area for displayingsaid difference in a direction of signal strength of said chromatogrambetween said adjacent data points of said base line.
 2. A chromatographcomprising: a detector for detecting a sample so as to output ameasuring signal according to elapsed time, an input unit for inputtinga strength parameter characterizing a form of base line by an operator,a data processor for processing said measuring signal based on saidinformation signal so as to output a chromatogram formed with aplurality of chromatogram data points and a base line corresponding tosaid chromatogram for correcting a plurality of data points forming saidbase line based on a first relation such that a difference between asignal data point of said chromatogram and a data point of said baseline corresponding to said chromatogram and/or a second relation suchthat a difference in a direction of signal strength of said chromatogrambetween adjacent data points of said base line, for connecting betweensaid corrected base lines by the spline interpolation method, and adisplay for displaying said chromatogram and said base line, saiddisplay having a flexibility display area for displaying said differencein direction of signal strength of said chromatogram between saidadjacent data points of said base line.